Process for catalytic partial oxidation reactions

ABSTRACT

Partial oxidation process of liquid and/or gaseous fuels, by means of a catalytic system, preferably consisting of oxides, nitrides or oxynitrides containing one or more elements selected from Rh, Ru, Ir, Pt, Ni, Fe, Co, Cr and Cu, comprising the following steps: —premixing and, upon start-up, preheating the reagents consisting of natural gas, oxygen or air or air enriched in oxygen, optionally vapour and/or CO 2 , to temperatures ranging from 150 to 600° C., below the flash-point values, so that the surface rate of the reaction gases is maintained above the flame rate and the temperature of the reagent mixture in the area preceding the catalytic bed is below its flash point; —reacting the reagent mixture in the reaction zone by interaction of the catalyst, activating it at temperatures ranging from 150 to 600° C. and at space velocities ranging from 50,000 to 5,000,000 Nl reagents/L cat×h, reaching temperatures ranging from 600 to 1350° C.

CROSS REFERENCE TO RELATED APPLICATION

This application is a 371 of PCT/EP03/005451, filed on May 21, 2003, andclaims priority to Italian Patent Application No. MI02A001133, filed onMay 24, 2002.

The present invention relates to a process for the production ofsynthesis gas (mixtures containing H₂ and CO) via Catalytic PartialOxidation (CPO) starting from a liquid and/or gaseous fuel and anoxidizing stream, consisting of oxygen, air or enriched air.

Production technologies of synthesis gas, (gas prevalently consisting ofa mixture of H₂ and CO with smaller quantities of H₂O, CO₂ and CH₄,whose content varies according to the fuel used and operatingconditions), and hydrogen have been developed for applications inlarge-scale plants dedicated, for example, to synthesis processes ofmethanol, ammonia and medium distillates. For these applications it isappropriate to carry out high pressure reactions in large capacityreactors.

The production technologies of synthesis gas have been continuouslyimproved in the last sixty years and although there are numerousvariations, they can be classified as technologies of:

-   a) non-catalytic partial oxidation (PO) of heavy hydrocarbons    (Falsetti, J. S. Hydrocarbon Technology International, 1993, page    57)-   b) steam and CO₂ reforming (SR) (Rostrup-Nielsen, J. R. “Catalytic    Steam Reforming”, in Catalysis Science and Technology, J. R.    Anderson, M. Boudart Eds. Vol. 5, Springer, Berlin 1988, page 1)-   c) autothermal reforming (ATR) (T. S. Christensen I. I. Primdahl,    Hydrocarbon Processing, March, 1994, page 39).

A technology which is still not widely used, but which is frequently theobject of R&S projects, is catalytic partial oxidation (CPO) with a lowcontact time. It allows synthesis gas to be produced from air and alarge number of hydrocarbon reagents without causing the formation ofbyproducts consisting of carbonaceous residues or NO_(x).

Catalytic partial oxidation with a low contact time is based on thereactionC_(n)H_(m) +nO₂ =nCO+m/2H₂ ΔH°<0  [1]

Production technologies of synthesis gas with a low contact time have sofar been used however for converting mixtures containing natural gas andoxygen.

We have discovered, however, process conditions and catalytic systemscapable of converting not only natural but also liquefied petroleum gas(LPG), liquid hydrocarbons such as naphthas and medium distillates (alsoin the presence of sulfurated compounds) and oxygenated compounds suchas methanol and dimethyl ether (DME), into synthesis gas.

In spite of the high costs, the use of some liquid hydrocarbons such asnaphtha in the production of hydrogen/synthesis gas is not uncommon:

-   -   for producing the hydrogen necessary for refinery operations;    -   in places where natural gas is not easily available;    -   when a low H₂/CO ratio must be used for example in the synthesis        of acetic acid or in other hydroformylation processes.

Catalytic reforming currently produces about 60% of the hydrogennecessary for refinery use and the remaining quantity is produced withsteam reforming. Non-catalytic partial oxidation, on the other hand, isthe preferred solution for treating heavier charges and producingsynthesis gas with a low H₂/CO ratio for hydroformylations.

The ATR technology which uses a burner followed by a combustion chamberand a catalytic bed can however only directly treat NG with limitationson the vapour/carbon and oxygen/carbon conditions in the feeding. WhenNG contains high quantities of C₂ ⁺ hydrocarbons, a pre-reformingpassage is necessary.

Our experimentation indicates that the CPO technology has thepossibility of also being used with liquid charges (naphtha alsocontaining sulfurated compounds) and has the possibility of convertingNG (also containing significant quantities of C₂ ⁺) using lowvapour/carbon and oxygen/carbon ratio values.

Due to its low energy consumption, low investment costs and facility ofuse, the CPO technology could therefore also be used for treating liquidhydrocarbons under advantageous conditions with respect to both steamreforming and non-catalytic partial oxidation.

A further use of the CPO technology is the pre-reforming of liquidhydrocarbon charges or natural gas containing high quantities of C₂ ⁺compounds. Pre-reforming carried out with O₂/C ratios<0.5 v/v allows C₂⁺ hydrocarbons to be transformed into mixtures of H₂, H₂O, CO, CO₂ andCH₄ which can then also be treated by the ATR technology.

The process, object of the present invention for the partial oxidationof liquid hydrocarbon fuels, selected from gasolines, naphthas andmedium distillates, and/or oxygenated products, selected from naturalgas and LPG, and/or gaseous products, selected from methanol, DME andethers, by means of a suitable catalytic system, comprises the followingsteps:

-   -   premixing and, upon start-up, preheating the reagents consisting        of natural gas, oxygen or air or air enriched in oxygen,        optionally vapour and/or CO₂, to temperatures ranging from 150        to 600° C., below the flash point values, so that the surface        rate of the reaction gases is maintained above the flame rate        and the temperature of the reagent mixture in the area preceding        the catalytic bed is below its flash point;    -   reacting the reagent mixture in the reaction zone by interaction        of the catalyst, activating it at temperatures ranging from 150        to 600° C. preferably between 250 and 450° and at space        velocities ranging from 50,000 to 5,000,000 Nl reagents/L cat×h,        preferably between 150,000 and 5,000,000 reaching temperatures        ranging from 700 to 1350° C.

The catalytic system preferably consists of oxides, nitrides oroxynitrides containing one or more elements selected from Rh, Ru, Ir,Pt, Ni, Fe, Co, Cr and Cu.

The element, or elements, contained in the oxides or nitrides oroxynitrides is preferably in a quantity ranging from 0.05 to 15% byweight.

The materials described above have generally shown considerableresistance to thermal shock, particularly significant under the reactionactivation conditions. These properties have proved to be higher thanthose of the oxide materials already used in CPO reactions. Furthermorethese catalytic materials have shown a higher activity, or analogoushowever, to that of the known materials.

The ratio between the moles of steam/moles of hydrocarbon carbon atoms(steam/C) preferably ranges from 0 to 3.5, more preferably from 0.1 to1.5, and the ratio between the moles of molecular oxygen/moles ofhydrocarbon carbon atoms (O₂/C) preferably ranges from 0.15 to 0.7, morepreferably from 0.25 to 0.65.

It has also been found that the process described above using acatalytic system preferably in the form of pellets, can give even betterresults when it is carried out with particular equipment, i.e. thereactor claimed by the same applicant in patent application[MI96/A000690], which allows catalytic partial oxidation reactions to beeffected at high pressures (10-50 atm) and space velocities(50,000-5,000,000 Nl/kg cat/h), maintaining the linear rates of thereagent gases at values higher than the flame rates, particularly in theinlet zone of the catalytic bed, also avoiding pressure drops due to theexpansion of the gaseous reaction mixture.

The equipment used substantially comprises four operating zones:

-   -   a feeding zone (A);    -   a distribution zone (B) with a constant or decreasing section        along the axis of the apparatus in the gas propagation        direction;    -   a reaction zone (C), consisting of a catalytic bed, with an        increasing section along the axis of the apparatus in the gas        propagation direction, communicating with said distribution zone        by means of a mutual transversal section;    -   a gas expansion zone (D).

Further details on this equipment are provided both in the patentapplication mentioned above [MI96/A000690] and in patent applicationMI98A000440 filed by the same applicant.

The CPO processes according to the invention can, as specified above, beused for pre-reforming: in this case the products obtained from thecatalytic partial oxidation, carried out between the reagents with anO₂/C volume ratio lower than 0.5, are sent to an autothermal reformingstep.

A further object of the present patent application relates to thecatalytic system itself for catalytic partial oxidation reactions whenthis is characterized in that it consists of nitrides or oxynitridescontaining an element selected from Ir and/or Pd.

The weight percentage of iridium and/or palladium preferably ranges from0.5 to 5%.

The known catalysts can consist of oxide carriers on which noble metalssuch as Rh, Ru, Ir, Pt and/or transition metals such as Ni, Fe, Co, aredeposited. The oxide carriers can consist of particles or monoliths withdifferent geometrical forms such as foam or honeycomb shapes.

The known catalysts can also consist of metallic sponges, metallicparticles with different geometries or metallic fibrous carriers onwhich the same metals are deposited.

The innovative catalysts described in the present document consist ofnitrides or oxynitrides containing noble metals and other transitionmetals such as Rh, Ru, Ir, Pt, Ni, Fe, Co. These metals can be supportedon nitride species as metallic aggregates but can also be included inthe chemical formula of nitride or oxynitride.

The nitrides can consist of:

-   -   AlN, Co₃N, Cr₂N, Fe₄N, Mn₄N, MoN, TiN, WN, VN    -   silicon nitride Si₃N₄ (F. K. Dijen, A. Kerber, U. Voigt, W.        Pfeiffer, M. Schulze, in “Key Engineering Materials” Vols.        89-91, M J. Hofmann P. F. Becher and G. Petzow Eds. TransTech.        1994, pages 19-28); H. Lange, G. Wotting H. Winter, Angew. Chem.        1991, 103, 1606)    -   Si—N—B systems or Si—B—N—C systems such as Si₃B₃N₇ and SiBN₃C        (H. P. Baldus and M. Jansen, Angew. Chem. Int. Ed. Engl. 1997,        36, 328)    -   systems consisting of layers of aluminum nitrides deposited on        oxide carriers by means of “atomic layer epitaxy” or “chemical        vapor deposition” with processes described in references        ((a) M. E. Bartram, T. A. Michalscke, J. W. Rogers, T. M. Mayer        Chem. Mater. 1991, 3, 353, (b) M. E. Bartram, T. A.        Michalscke, J. W. Rogers, R. T. Paine. Chem. Mater. 1993, 5,        1424, (c) C. Soto, V. Boiadjiev, W. T. Tysoe, Chem. Mater. 1996,        8, 2359).

The above materials are representative of but do not limit the group ofnitrides; the only limitations relate to the stability under thereaction conditions.

The systems cited above have in fact proved to have a considerableresistance to the thermal and mechanical stress which is produced duringthe start-up and stop reactions and also have a high thermal stabilityunder the reaction conditions also at temperatures exceeding 1000° C.

The nitrides AlN, CO₃N, Cr₂N, Fe₄N, Mn₄N, MoN, Si₃N₄, TiN, WN, VN, canbe prepared for example through the reactions [2-5] (The Chemistry ofTransition Metal Carbides and Nitrides, S. T. Oyama Ed., BlackieAcademic Professional, Glasgow, 1996)M_(x)O+C+½N₂→M_(x)N+CO  [2]M+NH₃→MN+ 3/2H₂  [3]MO+NH₃→MN+H₂O+½O₂  [4]MCl+N₂/H₂→MN+HCl  [5]M=Al, Cr, Ti, V, Mo, Mn, Co, Fe, W

The Si—N—B and Si—B—N—C systems such as Si₃B₃N₇ and SiBN₃C are preparedaccording to the reactions [6-9] (P. Baldus, M. Jansen, D. Sporn,Science 1999, 285, 699)Si(CH₃)₃—NH—Si(CH₃)₃+SiCl₄→Si(CH₃)₃—NH—SiCl₃+Cl—Si—(CH₃)  [6]Si(CH₃)₃—NH—SiCl₃+BCl₃→BCl₂—NH—SiCl₃+Cl—Si—(CH₃)  [7]

Systems consisting of layers of aluminum nitrides deposited on oxidecarriers (for example Al₂O₃) can, on the other hand, be obtained byconsecutive adsorptions of aluminum alkyls (for example Al(CH₃)₃) andammonia on oxide surfaces so as to obtain the reaction [10]. (A.Dabrowski “Adsorption and its application in industry and environmentalprotection, Studies in Surf. Sci and Catalysis 1999, 120A, 715; C. Soto,V. Bojadjiev, W. T. Tysoe Chem. Mater. 1996, 8, 2359)Al(CH₃)₃+NH₃→AlN+3CH₄  [10]

A further advantage of the nitride species consists in its having weaklybasic characteristics. These characteristics are advantageous as theyinhibit dehydrogenative cracking reactions of hydrocarbons.

Nitrides can contain in their molecular structure transition metalssuitable for catalyzing CPO reactions with a low contact time, but thesecan also be deposited on their surface with different techniques.

The first technique is impregnation with solutions of inorganic salts ofmetals followed by drying and calcination treatment.

A second technique consists in immerging particles of nitride oroxynitride in an organic solution of an organometallic compound such asRh₄(CO)₁₂, Rh₆(CO)₁₆, Rh(CH₃COCHCOCH₃)₃, Ru₃(CO)₁₂, Ir₄(CO)₁₂,Ir(CH₃COCHCOCH₃)₃, Pt(CH₃COCHCOCH₃)₂, CO₄(CO)₁₂, [C₅H₅Fe(CO)₂]₂,Ni(CH₃COCHCOCH₃)₂. The interaction between the organometallic moleculesdissolved in the organic solvent and the active sites of the nitride oroxynitride causes its decomposition and the anchorage of the metallicspecies onto the surface of the solid with a very high dispersiondegree. The solvent can then be removed and the solid dried. Thematerial thus obtained can already be used in CPO reactions without anyfurther thermal calcination treatment.

Some examples are provided which should not however be considered aslimiting the scope of the present invention.

EXAMPLES 1-2

The catalytic materials were tested in a tubular reactor with aninternal diameter equal to 15 mm. The reactor was made refractory andcan operate at high pressures and temperatures. Two ceramic foamymonoliths were used as thermal shield to prevent heat dispersions fromthe reaction zone towards the gas inlet and outlet area. The reactorallowed the heat produced in the reaction and the heat dispersed to bereduced to very low values and therefore has characteristics verysimilar to an adiabatic reactor. Two thermocouples, co-axiallypositioned at the beginning and at the end of the catalytic bed withrespect to the propagation of the reagents/products, allowed thetemperatures of the gases at the inlet and outlet of the catalytic bedto be monitored.

The tests were carried out at pressures ranging from 1.5 to 15 ATM, byfeeding heptane and air at a GHSV of 300,000 h⁻¹. The mixture ofproducts was analyzed by gaschromatography; furthermore an onlineparamagnetic detector allowed the possible presence of oxygen in theoutgoing stream to be monitored and also facilitated thestart-up/shutdown operations.

The catalyst used consisted of spheres of α-alumina (particle diameter-d_(p)- equal to 1.2 mm) on which Rh species were deposited by means ofa solid-liquid reaction obtained by dripping a solution of n-heptanecontaining Rh₄(CO)₁₂ onto the solids. The clusters of Rh in contact withthe alumina spheres become fixed to the solid surfaces by decomposingand the phenomenon can be visually followed as it causes adiscolouration of the initially reddish-orange solution. At this point,the colourless solution is eliminated and the alumina spheres containing1% by weight of Rh, dried. The material thus obtained was charged intothe reactor and used as catalyst.

Table 1 includes the inlet and outlet compositions of two reactivitytests obtained by preheating and premixing streams of air and n-heptaneand sending them to the reaction zone with a stream so as to have a GHSVof 300000 h⁻¹.

Following the activation of the reaction and after reaching stationaryreactivity conditions, H₂S was added to the stream of n-heptane and airin order to obtain a concentration of sulfur in the hydrocarbon streamof 300 ppm. It is therefore possible to verify that the addition of H₂Shas not caused the deactivation of the catalyst.

EXAMPLES 3-4

The reactor solutions and operating conditions described in Examples 1-2were adopted, using n-octane as hydrocarbon reagent and catalyticsystems obtained by depositing 1% of Rh on a spheroidal carrierconsisting of N₄Si₃. Also in this case, the deposition of the Rh specieswas obtained as described in Examples 1-2 by decomposing clusters ofRh₄(CO)₁₂ contained in a solution of n-heptane on the surfaces of thenitrides. After drying, the catalyst was charged into the reactorwithout further thermal treatment.

Table 2 contains the reactivity data obtained in two tests effected atpressures of 1.5 and 15 ATM by introducing the premixed and preheatedgases into the reactors and using reagent streams so as to have aGHSV=300000 h⁻¹. Also in this case, after reaching stationary reactivityconditions, it was verified that neither the deactivation of thecatalyst nor a variation in the reactivity characteristics had beencaused by co-feeding H₂S so as to obtain a concentration of 300 ppm inthe hydrocarbon stream.

EXAMPLES 5-6

In these cases, the partial oxidation reactions were carried out in arefractory reactor containing a distribution zone and a catalytic zoneboth conical (hourglass configuration). The distribution zone has aninlet diameter of 15 mm and a height of 10 mm. The catalytic zone has aninlet diameter of 4 mm, a height of 18 mm and an outlet diameter of 20mm. The catalytic pellets were positioned between two areas filled withceramic material, acting as thermal shield, and consisted respectivelyof pellets of alpha-Al₂O₃ in the gas inlet zone and a ceramic monolithagain of alpha-Al₂O₃ downstream of the catalytic bed. Two thermocouples,positioned longitudinally to the inlet and outlet of the catalytic bed,monitored the gas inlet and outlet temperature. The tests were carriedout at pressures of 1.5 and 15 ATM.

The catalyst was obtained by depositing 0.5% of Ru and 0.5% of Rh ontopellets of AlN, using a solution in n-hexane of clusters of Rh₄(CO)₁₂and Ru₃(CO)₁₂ with the procedures described in the previous examples.

The composition of the mixture of reagents and products obtained isdescribed in Table 3.

Also in this case the introduction of 300 ppm of H₂S in the hydrocarbonstream did not cause variations in the composition of the products.

EXAMPLE 7

The catalytic partial oxidation reactions were carried out in a conicalreactor like that described in the previous example, using a bimetalliccatalyst containing Rh (0.5% by weight) and Ru (0.5% by weight) preparedaccording to the procedure of Examples 5 and 6 but using as carrierparticles with an average diameter of 1 mm consisting of boron nitride.Pre-reforming reactions of n-heptane were effected on this material,using a reagent mixture consisting of n-heptane and pure oxygen so as toobtain an O₂/C ratio=0.3 v/v and a GHSV=400000 hours⁻¹.

Table 4 contains the composition of the in-going mixture and of themixture of reaction products.

TABLE 1 1.5 ATM 15 ATM X moles in X moles out X moles out  1 METHANE0.000 0.000 0.007  2 CO 0.000 0.219 0.213  3 CO₂ 0.000 0.010 0.012  9 O₂0.190 0.000 0.000 10 H₂0 0.000 0.016 0.021 11 H₂ 0.000 0.245 0.230 12 N₂0.761 0.510 0.517 13 HEPTANE 0.049 0.000 0.000

TABLE 2 1.5 ATM 15 ATM X moles in X moles out X moles out  1 METHANE0.000 0.000 0.005  2 CO 0.000 0.218 0.213  3 CO₂ 0.000 0.010 0.012  9 O₂0.191 0.000 0.000 10 H₂0 0.000 0.018 0.022 11 H₂ 0.000 0.239 0.228 12 N₂0.766 0.514 0.520 14 OCTANE 0.043 0.000 0.000

TABLE 3 1.5 ATM 15 ATM X moles in X moles out X moles out T = 150° C.0.000 0.000 0.000 0.000 0.217 0.216 0.000 0.013 0.014 0.000 0.000 0.0000.000 0.000 0.000 0.204 0.000 0.000 0.000 0.030 0.030 0.000 0.229 0.2280.766 0.512 0.513 0.000 0.000 0.000 0.043 0.000 0.000

TABLE 4 10 ATM X moles in X moles out T = 125° C. T = 1267° C.  1METHANE 0.000 0.397  2 CO 0.000 0.447  3 CO₂ 0.000 0.000  6 ETHANE 0.0000.004  8 PROPANE 0.000 0.000  9 O₂ 0.677 0.000 10 H₂O 0.000 0.000 11 H₂0.000 0.152 12 N₂ 0.000 0.000 13 HEPTANE 0.323 0.000 14 OCTANE 0.0000.000

1. A partial oxidation process of liquid hydrocarbon fuels comprising at least one member selected from the group consisting of gasolines, naphthas and medium distillates by a catalytic system, comprising: premixing and, upon start-up, preheating reagents comprising liquid hydrocarbon fuels and oxygen, air or air enriched in oxygen to temperatures ranging from 150 to 600° C., below the flash point values, so that the surface rate of the reaction gases is maintained above the flame rate and the temperature of the reagent mixture in the area preceding the catalytic system is below its flash point, thereby forming a reagent mixture; reacting the reagent mixture in a reaction zone and in the presence of the catalyst at temperatures ranging from 150 to 600° C. and at space velocities ranging from 50,000 to 5,000,000 Nl reagents/L cat×h, and increasing the temperature to a value ranging from 700 to 1350° C., wherein the catalytic system comprises nitrides or oxynitrides that contain a at least one metal selected from the group consisting of Rh, Ru, Ir, Pt, Ni, Fe, Co, Cr, and Cu.
 2. A partial oxidation process of gaseous fuels, selected from the group consisting of natural gas and LPG, by a catalytic system comprising nitrides or oxynitrides containing at least one element selected from the group consisting of Rh, Ru, Ir, Ni, Fe, Co, Cr and Cu, comprising: premixing and, upon start-up, preheating the reagents comprising natural gas, oxygen, air, or air enriched in oxygen to temperatures ranging from 150 to 600° C., below the flash point values, so that the surface rate of the reaction gases is maintained above the flame rate and the temperature of the reagent mixture in the area preceding the catalytic system is below its flash point, thereby forming a reagent mixture; reacting the reagent mixture in the reaction zone in the presence of the catalyst and at temperatures ranging from 150 to 600° C. and at space velocities ranging from 50,000 to 5,000,000 Nl reagents/L cat×h, and increasing the temperature to a value ranging from 700 to 1350° C.
 3. The process according to claim 1, wherein the at least one metal contained in the nitrides or oxynitrides is present in a quantity ranging from 0.05 to 15% by weight.
 4. The process according to claim 1, wherein the reaction occurs at temperatures ranging from 250 to 450° C., whereas the space velocities range from 150,000 to 5,000,000 Nl reagents/L cat×h.
 5. The process according to claim 1, wherein, between the reagents, the ratio between the moles of steam/moles of hydrocarbon carbon atoms (steam/C) ranges from 0 to 3.5 and the ratio between the moles of molecular oxygen/moles of hydrocarbon carbon atoms (O₂/C) ranges from 0.15 to 0.7.
 6. The process according to claim 1, wherein the ratio between the moles of steam/moles of hydrocarbon carbon atoms (steam/C) ranges from 0.1 to 1.5 and the ratio between the moles of molecular oxygen/moles of hydrocarbon carbon atoms (O₂/C) ranges from 0.4 to 0.6.
 7. A catalytic system for catalytic partial oxidation reactions comprising nitrides or oxynitrides containing Ir and Pd.
 8. The catalytic system according to claim 7, wherein the weight percentage of iridium and palladium ranges from 0.5 to 5%.
 9. The process according to claim 1, further comprising autothermal reforming the products obtained from the catalytic partial oxidation, effected between the reagents with an O₂/C volume ratio lower than 0.5.
 10. The process according to claim 2, wherein the reaction occurs at temperatures ranging from 250 to 450° C., whereas the space velocities range from 150,000 to 5,000,000 Nl reagents/L cat×h.
 11. The process according to claim 2, wherein, between the reagents, the ratio between the moles of steam/moles of hydrocarbon carbon atoms (steam/C) ranges from 0 to 3.5 and the ratio between the moles of molecular oxygen/moles of hydrocarbon carbon atoms (O₂/C) ranges from 0.15 to 0.7.
 12. The process according to claim 2, wherein the ration between the moles of steam/moles of hydrocarbon carbon atoms (steam/C) ranges from 0.1 to 1.5 and the ratio between the moles of molecular oxygen/moles of hydrocarbon carbon atoms (O₂/C) ranges from 0.4 to 0.6.
 13. The process according to claim 2, further comprising autothermal reforming the products obtained from the catalytic partial oxidation, effected between the reagents with an O₂/C volume ratio lower than 0.5.
 14. The process according to claim 2, wherein the catalytic system further comprises nitrides or oxynitrides which contain Pt.
 15. The process according to claim 2, wherein the at least one element contained in the nitrides or oxynitrides is present in a quantity ranging from 0.05 to 15% by weight.
 16. The process according to claim 1, wherein the reagents further comprise vapour and CO₂.
 17. The process according to claim 2, wherein the reagents further comprise vapour and CO₂.
 18. The process according to claim 1, wherein the liquid hydrocarbon fuels further comprises at least one oxygenated product selected from the group consisting of methanol, DME, and ethers.
 19. The process according to claim 1, wherein the catalytic system comprises at least one layer of an aluminium nitride deposited on oxide carriers. 